A spade may be made of any size, and if the same number of strokes be made in the hour, the requisite exertion will vary nearly as the cube of the le… - William Stanley Jevons

What capital I give for the spade merely replaces what the manufacturer had already invested in the expectation that the spade would be needed.

All acts of reasoning seem to me to be different cases of one uniform process which may perhaps be best described as the substitution of similars. ..The chief difficulty consists in showing that all the forms of the old logic, as well as the fundamental rules of mathematical reasoning, may be explained upon the same principle; and it is to this difficult task I have devoted the most attention.

A correct theory is the first step towards improvement, by showing what we need and what we might accomplish.